From US Pat. App. Pub. 2009/0139991 A1 an actuator element for the alternating opening and closing of a motor vehicle tank cover as a consequence of successive actuations in closing direction it is known that if the closed cover is pushed down in closing direction, cams of a plunger are rotated through sloping ramp surfaces of a guide and engage in long axial grooves of the guide when released, so that an axial spring can drive out the plunger against the closing direction and open out the cover. Through renewed pressing down the cams are rotated further and engage in short axial grooves of the guide when released, which prevent an extension of the plunger. Through successive actuations in closing direction, the cams thus rotate endlessly in a rotational direction and alternately engage in the short and long axial grooves, which for this purpose alternate in circumferential direction.